Update AGENTS.md files across multiple modules to standardize task status update instructions and introduce a new document for Secret Leak Detection operations.

- Modified task status update instructions in AGENTS.md files to refer to corresponding sprint files as `/docs/implplan/SPRINT_*.md` instead of `docs/implplan/SPRINTS.md`.
- Added a comprehensive document for Secret Leak Detection operations detailing scope, prerequisites, rule bundle lifecycle, enabling the analyzer, policy patterns, observability, troubleshooting, and references.

src/Bench/StellaOps.Bench/AGENTS.md

@@ -19,7 +19,7 @@ Design and maintain deterministic benchmark suites that measure StellaOps perfor
 - Existing benchmark notes in `docs/dev/perf/` (if present) and any sprint-specific design docs referenced by TASKS.
 
 ## Working Agreement
-1. **State sync**: mark tasks `DOING`/`DONE` in both `docs/implplan/SPRINTS.md` and `src/Bench/StellaOps.Bench/TASKS.md` before/after work.
+1. **State sync**: mark tasks `DOING`/`DONE` in both corresponding sprint file `docs/implplan/SPRINT_*.md` and `src/Bench/StellaOps.Bench/TASKS.md` before/after work.
 2. **Baseline references**: link commits/results for baseline metrics; update docs when targets shift.
 3. **Deterministic harnesses**: avoid random seeds without explicit seeding; ensure benchmarks run offline with local fixtures.
 4. **Safety**: guard against resource exhaustion—cap concurrency, add cleanup/finalizers, ensure containerised runs have limits.